This invention relates to molded plastic components and, in particular, to molded plastic components having enhanced surface finish.
Plastic components can be molded in a wide variety of molds such as injection molds, compression molds, vacuum molds, RIM molds, and blow molds. A common problem in the molding of plastic components is that the solidified plastic component often sticks to the component-defining surfaces of the mold. As a result, the mold cycle times are unnecessarily extended. Also, the article-defining surface as well as the resin flow path within the mold must be cleaned and/or lubricated on a periodic basis to ensure that subsequently molded plastic components are not contaminated with plastic that was previously stuck within the mold. This problem is especially acute where color of the plastic component has been changed.
One way of reducing this sticking problem is to utilize a mold release spray or lubricant wherein the spray is deposited on the surface layers which define the article-defining cavity. However, the use of such a spray is not only time-consuming but expensive.
Another way of reducing the sticking within the article-defining cavity is to incorporate release agents within the plastic itself. However, the use of such release agents present other problems including the expense of incorporating such release agents within the plastic material.
Another way of reducing the sticking problem is to use increased molding pressures. However, here again, the use of increased molding pressures adds even more problems to the molding process.
The U.S. patent to Iwami et al. U.S. Pat. No. 5,468,141 discloses a core block including a release insulating layer on a cavity side thereof wherein the release insulating layer is made of a material selected from the group consisting of fluorocarbon resins, fluorocarbon resin composite materials, silicon resin composite materials, and metal platings with fluorocarbon resin dispersion. The patent is concerned with developing a new molding technology for obtaining good articles at a relatively low pressure.
The U.S. patent to Baumgartner et al. U.S. Pat. No. 5,535,980 discloses a mold having an insulating layer and a second layer of metal particles suspended in resin deposited on the insulating layer. The patent is concerned with a procedure for producing a metal surface on a layer of low thermoconductivity.
An object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having at lest one self-lubricating surface layer which provides at least one substantially non-stick surface to eliminate the need to spray the interior of the mold with a lubricant.
Another object of the present invention is to provide a molded plastic component having enhanced surface finish and which is molded within a mold having at lest one self-lubricating surface layer which allow the molding of the plastic component at reduced cycle times.
Still another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded in a mold having at least one self-lubricating surface layer which has an optimum combination of release (non-stick), low friction, dry lubrication, corrosion resistance, wear resistance, and hardness properties that typically could not be provided or maintained from traditional plating, solid film lubricants and coatings.
Another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having at least one self-lubricating surface layer which allows the use of reduced molding pressures, enhances plastic flow and flow pressures within the mold and reduces plastic flow and nit lines.
It is another object of the present invention to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having a relatively thin, self-lubricating surface layer formed on at least one interior, component-defining surface of the mold.
Yet still another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having a self-lubricating surface layer which eliminates or reduces the need to formulate the plastic of the plastic component to include a release agent.
Still another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having a self-lubricating surface layer formed on substantially all mold components including cavity, core, slides, lifters, core pins, manifolds, mixer blocks, nozzles, sprue bushings, ribs, bosses, etc. The surface layer may be formed on one or more ejector pins of the mold which, in turn, help to define the mold cavity in which the plastic component is molded.
Another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having a self-lubricating surface layer which defines a water line wherein impurities within the water flowing through the water line do not build-up within the water line to ensure the proper functioning of the mold whereby the plastic component is properly molded in the mold.
Yet still another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having an exterior, self-lubricating surface layer which allows the exterior of the mold to be cleaned very quickly thereby reducing down time of the mold.
It is still another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having a self-lubricating surface layer which does not flake during use of the mold.
Yet still another object of the present invention is to provide a molded plastic component having enhanced surface finish wherein the plastic component is molded within a mold having a self-lubricating surface layer which is compatible for use in injection molds, Reaction Injection Molding (RIM), compression molds and vacuum molds and wherein the plastic may include such plastics as DYM(copyright) polyester elastomers available from DuPont, acrylonitrile-butadiene-styrene (ABS), SANTOPRENE(copyright) thermoplastic elastomer available from Advanced Elastomer Systems, polypropylene, sheet molding compound (SMC), thermoplastic olefin elastomer (TPO), thermoplastic polyurethane (TPU) and other plastic compounds such as polyurethane or polyurea.
In carrying out the above objects and other objects of the present invention, a plastic component molded within a mold having at least one metal base, a mold cavity, and at least one self-lubricating surface layer having a substantially uniform thickness and which defines the plastic component within the mold cavity is provided. The at least one self-lubricating surface layer includes a porous metallic skin integrally connected to and extending from an interior surface of the at least one metal base and lubricating particles disposed on the skin and in pores of the skin. The lubricating particles are bonded together to form a sealed surface of the at least one surface layer. In this way, the molded plastic component has an enhanced surface finish.
Preferably, the interior surface of the at least one metal base has substantially the same shape as the sealed surface.
Also, preferably, the surface layer has a substantially uniform thickness in the range of 0.0007 to 0.001 inches. Still preferably, the substantially uniform thickness is approximately 0.001 inches.
The metallic skin typically includes a plurality of sinusoidally-shaped projections. Also, preferably, the metallic skin is a nickel alloy such as an autocatalytic nickel alloy.
The lubricating particles are preferably submicron-sized particles of low friction fluoropolymers.
The plastic component may be injection molded, compression molded, or blow molded when the mold has a pair of metal bases and wherein each of the metal bases has a self-lubricating surface layer as described above. When the plastic component is vacuum molded, only a single metal base need be provided with a single, self-lubricating surface layer described above.
The plastic of the plastic component may comprise such plastics such as DYM, ABS, SANTOPRENE(copyright) thermoplastic elastomer available from Advanced Elastomer Systems, polypropylene, SMC (with glass filler), TPO, TPU and other plastic compounds.
When the mold is an injection mold having an ejector pin, the ejector pin also has a self-lubricating surface layer as described above which helps to define the mold cavity.
Also, when the mold is an injection mold, the mold may have a core pin having a self-lubricating surface layer as described above which also helps to define the mold cavity.
The mold may have a cooling line formed therein the at least one metal base wherein the cooling line has a self-lubricating surface layer also as described above.
When the mold has a resin flow path extending from an outer surface of the mold to the mold cavity, the resin flow path may also have a self-lubricating surface layer as described above. Also, the outer surface of the mold may also have a self-lubricating surface layer as described above.
The advantages accruing to the molded plastic component having enhanced surface finish are numerous. For example, the enhanced surface finish can be provided using lower molding pressures, reduced cycle time and without the need for the use of release agents either on the component-defining surface of the mold or within the plastic itself.